Rocknitive Embedded Coding Challenge

The aim of this coding challenge is to prove general development skills and basic understanding of the typical challenges in embedded development.

Task

In this challenge you are required to handle communication over a (simulated) serial interface. Your program must have the following features:

• Receive data via a (simulated) interrupt.
• Parse incoming data for messages defined in the protocol below.
• Send the required responses.
• Print all messages (received and sent) in a human readable format to the console.

Upload your solution as a git repository to one of the public platforms (e.g. GitHub or Bitbucket).

Protocol

• Messages are encoded as binary TLV (type-length-value) messages.
• The type and length field are encoded as the higher and lower four bits, respectively, of the first byte of each message.
• The value contains the payload with as many bytes as given by the length value.

Message types

Type	Length	Name	Payload
1	0	Empty	None
2	4	Add	Two 16-bit unsigned integers
3	2	Result	One 16-bit unsigned integer
4	3	Delay	16-bit unsigned integer and opaque data byte
5	1	Timeout	Opaque data byte
6	N	Log	String of N ASCII encoded characters

Responses

• Respond to Empty messages with an Empty message.
• Respond to Add message with a Result message containing the sum of the numbers in the Add message.
• Respond to Delay messages with a Timeout message. The integer in the Delay message represents a duration in milliseconds. The Timeout message should be send after this duration has elapsed. The payload of the Timeout message should contain the data byte received with the Delay message.

Additional information

• Add your code in src/challenge.c, none of the other source file should be modified.
• The project is built using CMake and GCC. If you add additional source files they need to be added to the CMakeLists.txt file.
• All data must be encoded in network byte-order, i.e. big-endian.
• This challenge uses FreeRTOS (Posix-Port) to simulate hardware interrupts and preemption on a desktop machine.
• You can also use FreeRTOS features to implement your solution. This is recommended, but not mandatory.
• The test cases don't contain multiple pending delays simultaneously, but you get bonus points if your solution could handle that.

Installation / Dependencies

• Install dependencies:
  • Windows: Use the Windows-Subsytem for Linux (WSL) and do the same as on Ubuntu.
  • Ubuntu: sudo apt-get install git cmake
  • MacOS: brew install git cmake
• Clone the repository: git clone ...
• Create a build directory mkdir build && cd build
• Setup build: cmake ..
• Build: make
• Run: ./coding_challenge